The US military is developing software that will let it secretly manipulate social media using fake online personas designed to influence internet conversations and spread pro-American propaganda.

A Californian corporation has been awarded a contract with the US Central Command (Centcom) to develop what is described as an "online persona management service" that will allow one serviceman or woman to control up to 10 separate identities at once.

The contract stipulates each persona must have a convincing background, history and supporting details, and that up to 50 controllers must be able to operate false identities from their workstations "without fear of being discovered by sophisticated adversaries".

The project has been likened by web experts to China's attempts to control and restrict free speech on the internet.